(1) Field of the Invention
The present invention relates to a method for the thermal decomposition of a fluid toxic substance, especially dioxins and furans, contained in a gas, such as a flue gas, in an apparatus which comprises a substantially cylindrical main combustion chamber, a secondary combustion chamber arranged thereabove, an inlet opening leading into the main combustion chamber preferably at an angle to a tangential plane for introducing a stream of the gas containing the toxic substance with an angular momentum into the main combustion chamber, and a burner arranged to direct a flame into the main combustion chamber for subjecting the gas containing the toxic substance to combustion. An annular gas stream retaining device is arranged above the burner, the retaining device defining a central opening permitting the stream of gas to pass from the main combustion chamber into the secondary combustion chamber, the central opening having a diameter smaller than that of the cylindrical main combustion chamber, and the retaining device comprises obliquely downwardly directed nozzle means.
(2) Description of the Prior Art
Certain highly toxic organic substances, such as dioxins and furans, can be economically disposed of only by thermally decomposing them into less problematic compounds at high temperatures. Published German Pat. application No. 2,357,804, for example, discloses a combustion apparatus comprising burners operated by fuels, such as natural gas or the like, for thermally decomposing such toxic substances. Combustion chambers of large volume are required to assure a dwell time of sufficient length to permit combustion of the substances in a high-temperature zone. Such furnaces are correspondingly expensive and, in addition, it is difficult to achieve a suitable mixing and turbulence of the gas stream in the combustion chamber to assure the desired thermal decomposition. If the volume of the combustion chamber is reduced, the dwell time of the toxic substances in the zone of high temperature is too short to permit the decomposition reactions to be fully completed.